The invention relates to a method and apparatus for weighing by conveyor-type weighing unit, where a conveyor belt forming an endless loop is transported along a first guiding unit, defining a first conveying direction and extending in-between the top sides of opposite arranged rollers. The belt is driving in a revolving manner by a driving unit and transported over a weighing device in a downstream direction. The weighing device being a part of the first guiding unit and performs weighing of objects transported along the conveyor.
Conveyor weighing has been known weighing technique for quite some time. Such apparatus have mainly been used for weighing of bulk material such as grain, rocks and other like materials. There is a growing need for accurate and high speed weighing units, both continuous weighing of bulk material as well as for weighing of individual objects such as food pieces. It is essential in the food processing to measure as exact as possible the weight of the object being processed prior to various type""s of operations such as sorting, cutting, or packaging, The weighing of individual food pieces transported along a conveyor is today an important operation in processing of f.ex. fish filets and trimming of meat to mention two. If one had to weigh every object individually on a stationary weighing unit, the processing capacity would be diminished dramatically. There is however no question that the aforementioned applies not only to processing of fish and meat but also to other types of food and/or objects.
The main disadvantage of the existing conveyor-type weighing apparatus, especially those available for the food processing industry is lack of accuracy and low processing capacity. Further disadvantage as commonly known, is the use of one weighing platform, where the length of the platform determines the processing capacity of the weighing apparatus. If a number of single objects, are to be weighed successively and without disturbance to a next adjacent object the distance between two successive objects must be equal or greater than the length of the platform. This results in low processing capacity as the maximum length of platform needed determines the distance between adjacent objects. One can only increase the processing speed by decreasing the length of the weighing platform. By decreasing the length of a platform a larger number of objects can not be successively weighed. On the other hand by increasing the length of a platform, the distance between the objects on the conveyor must be increased and thereby the process capacity will be decreased.
From U.S. Pat. No. 4,526,244, it is known to use three or more, but spaced apart weighing stations or areas disposed along a conveying path and a comparator (computer) for comparing the weighings from each weighing station. However, the 244 Patent does not teach the use of side by side arrangement of weighing platforms.
The object of the invention is to provide an accurate and high-speed conveyor-type weighing unit capable of weighing objects of varying dimension at high-speed and operating performance.
The conveyor-type weighing unit according to the invention is characterised in; the weighing device comprising;
two or more side by side, in a conveying direction arranged weighing platforms, each platform having a pre-defined platform length, each weighing platform continuously weighing the conveyor belt section placed thereover and the object transported thereon. One or more adjacent arranged weighing platforms may constitute at each time a weighing unit having a total platform length equal or greater than the object length to be weighed, said weighing platforms being operatively connected to a data processing unit, said data processing unit receiving and processing data from said weighing platforms, and based thereupon, the length/weight of the object is determined and an accordingly appropriate number of adjacent platforms selected, having total length at least equal or greater than the object to be weighed and thereby enabling minimal spacing between adjacent objects and maximum operational capacity.
As a result it is possible to perform weighings of objects of varying length with a minimum distance between the objects, and thereby obtain high processing speed. By this arrangement, the distance between adjacent objects only needs to be equal or larger than the length of one of the platforms or added length of two or more adjacent platforms. By this arrangement, objects of varying length can be weighed with minimum distance between them at high speed and with great accuracy.
The invention is moreover characterised in that a predetermined limit is when the first derivative of two successive measurements equals to zero.
The invention is further characterised in that the number of weighing platforms may be three or more.
Moreover according to the invention it is particularly preferred that the platforms have different length.
According to the invention, it is particularly preferred that the number of platforms may be unlimited.
Moreover, the number of platforms may be unlimited and two or more of the platforms may form a weighing unit whose added platform length is larger than the length of the object to be weighed.
Finally, according to the invention, a method is characterised in that the object is moved along the conveyor belt in a downstream direction over a weighing device comprising two or more weighing platforms. The platforms are arranged side by side in the downstream direction. Each of the platforms continuously measure the weight of the conveyor belt transported over them. The weighing measurements are continuously sent to a data processing unit, where the measurements from one or more platforms are processed and continuously compared. If a certain number of repeated measurements from the platforms forms a weighing measurements within a prescribed minimum time and/or weighing range, such measurement represent the weighing of the respective object.
Moreover according to the invention it is particularly preferred that the prescribed time- and/or weighing minimum is when the first derivative (xcex94y/xcex94x) of two or more repeated weighing measurements equal to zero, then such measurement constitute the weighing of the object.
And last according to the invention it is particularly preferred that the prescribed time and/or weighing minimum is when the first derivative (xcex94y/xcex94x) of the added weighing of two or more weighing platforms equal to zero, then such measurement constitute the weighing of the object.